Among the conventionally-known tailgate-equipped vehicle body structures is one disclosed, for example, in Japanese Patent Application Laid-open Publication No. 2014-12445 (hereinafter referred to as “the relevant patent literature”), in which the tailgate for opening and closing a rear opening section is provided on a rear section of the vehicle and a sub door is provided on the tailgate so that a sub door opening section formed in the tailgate is opened and closed by the sub door. When the tailgate is in the closed position, the sub door opening is located rearward of the rear opening section. With the tailgate kept in the closed position, a passenger can get in and out the vehicle, through the sub door opening section and the rear opening section, by opening the sub door opening section with the sub door.
With the tailgate-equipped vehicle body structure disclosed in the relevant patent literature, where the rear opening section is provided in the rear section of the vehicle and the sub door opening section is formed in the tailgate, a level difference would be formed between a lower edge portion of the sub door opening section and a lower edge portion of the rear opening section. Such a level difference between the lower edges portions of the sub door opening section and the rear opening section may undesirably prevent passengers from smoothly getting in and out of the vehicle and prevent baggage from being smoothly loaded and unloaded to and from the vehicle.